Ball joint element and method of forming same

ABSTRACT

An improved, light weight ball member for universal connections having a hollow interior both in its ball portion and connecting portion for providing high strength and light weight and method for forming it through an improved forging process, using improved forging dies.

PRIORITY INFORMATION

This is a Divisional Application of U.S. patent application Ser. No.11/872,187, filed Oct. 15, 2007, which is based on and claims priorityto Japanese Patent Application No. 2006-283509 filed Oct. 18, 2006, theentire contents of both of which is hereby expressly incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved ball joint and method of formingone.

2. Description of the Related Art

Ball joints are used in a large number of applications for providingpivotal connections that transmit motion for one connected member toanother, particularly when the relationship of the connected elementschanges during the motion transmission. A typical application in whichthis invention may be utilized is shown in FIG. 1, that illustrates inperspective a steering arrangement for a wheel of a dirigible frontwheel suspension for a vehicle, such as an automobile. Only the steeringsystem of the vehicle is shown, as it is believed that those skilled inthe art how the ball joint constructed and manufactured in accordancewith the invention may be used in such combinations. Those skilled inthe art will also understand that ball joint elements constructed andmanufactured in accordance with the invention are capable of use inother combinations using joints of this general type.

The vehicle steering system, indicated generally at 11, includes asteering wheel 12 is positioned in a known manner in the driver'scompartment of the vehicle. Greater detail of the vehicle is not shownas noted above to permit easier understanding of a typical applicationof the invention. The steering wheel 12 is connected to the upper end ofa steering shaft 13 that extends at least in part outside of thedriver's compartment typically into the vehicle engine compartment.

There it is connected to a steering box 14 for effecting controlrotation of a steering pitman arm 15. The outer end of the pitman arm 15carries, in a manner to be described later, to a ball joint element,indicated generally by the reference numeral 16 constructed andconfigured in accordance with the invention, as will be described later,by reference to the remaining figures.

The ball joint 16 forms a universal pivotal connection to a linkagesystem including links 17, 18 and 19 with like ball joints 16 providingthe pivotal connections between the directly connected ends of thelinks. The final pivotal connection is to the supporting element 21 thatjournals a wheel 22 for both rotation about the wheel axis and forsuspension and steering movement, as is well known in the art.

From the foregoing description it should be readily apparent that a balljoint must be capable of providing smooth transmission of movementbetween connected members with a minimum of friction. Also in manyapplications such as in vehicle steering linkages it should be robustand also light in weight. The latter desired condition is because itforms a portion of what is referred to as unsprung weight. Also a lowcost of fabrication from a strong material is desired.

FIG. 2 illustrates a prior art attempt at achieving these goals. Thistype of ball joint is used in a large number in the steering system ofvehicles and is typified in Japanese Published ApplicationJP-A-2005-31605. The essential part of this prior art type ball joint iscomprised generally of a ball joint member 101 rotatably contained in acasing 102. The ball joint member 101 comprised of a smooth ball portion101 a having a spherical sliding surface 101 b suitably journalled inthe casing 102 and a connecting shaft 101 c extending in radialdirection from part of the smooth ball portion 101 a.

Recently it has been recognized that in such ball joints, there isdesired a reduction in excess material to save resources and reduceweight. A typical method known for this purpose is to provide a weightreducing hole 101 d in the smooth ball portion 101 a of the ball jointmember 101. The hole is bored along the axis from the opposite side ofthe connecting shaft 101 c by forging or machining.

However, if the diameter of weight reducing hole 101 d in the ball jointmember 101 is enlarged to provide the weight reduction, the slidingsurface area of the smooth ball portion decreases, resulting inrestricted pivoting angle of the connecting shaft possible. Therefore,there is a restriction to the increase in the size of the weightreducing hole 101 d. Alternatively, while it is possible to enlarge theweight reducing hole 101 d by machining the inside surface 101 b with acutting tool bit inserted through the opening of the weight reducinghole 101 d, the number of machining steps increases and the time offorming increases, which is a factor of increasing manufacturing cost.Therefore, this method is hard to practice.

It is, therefore, a principal object of this invention to provide alight weight, strong ball joint having a large spherical surface and alow cost method of forming it.

SUMMARY OF THE INVENTION

A first feature of the invention is adapted to be embodied in a ballmember for a ball and joint pivotal connection being formed from asingle piece comprised of a ball portion adapted to be pivotallyconnected within a socket formed by one of the elements to be connectedand a shank portion adapted to be fixedly secured in a complimentaryopening of the other element to be pivotally connected. The ball memberhas an inner cavity complimentary in shape to said ball and shankportions and closed at both ends.

Another feature of the invention is adapted to be embodied in a methodof forming a ball member for a ball and joint pivotal connection formedfrom a single piece comprised of a ball portion adapted to be pivotallyconnected within a socket formed by one of the elements to be connectedand an integral shank portion adapted to be fixedly secured in acomplimentary opening of the other element to be pivotally connected.The method comprises the steps of forging a solid cylindrical piece ofmetal into the integral ball and shank portions with complimentaryclosed ball shaped and cylindrical shaped cavities by forging steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a typical embodiment in which theinvention may be employed.

FIG. 2 is a cross sectional view showing a prior art type of ball jointelement.

FIG. 3 is a perspective view of a ball joint embodying the inventionlooking from the shank end and made in accordance with an embodiment ofthe invention.

FIG. 4 is a perspective view of a ball joint looking from the ball endand made in accordance with an embodiment of the invention.

FIG. 5 is cross sectional views taken through a forged material beforeforming into the final product

FIG. 6 is a cross sectional view of the final product incorporating theinvention.

FIG. 7 is a series of cross sectional views showing in the upper portionthereof the shape of the ball joint element during the various forgingsteps and in the lower portion thereof the forging dies that perform theforging steps.

DETAILED DESCRIPTION OF THE INVENTION

Referring now in detail to the drawings and initially to FIGS. 3 and 4,these are perspective views of a ball joint element configured andmanufactured in accordance with the invention. The novel ball jointmember is indicated generally by the reference numeral 31, made in amanner to be described shortly by reference to FIGS. 5-7, and iscomprised of a smooth ball portion 32 having a spherical journalingsurface and a connecting shaft portion 33 provided to project radiallyfrom the outer surface of the smooth ball portion 32. The smooth ballportion 32 and the connecting shaft portion 33 are made by applyingmachining processes such as cutting, rolling and other plastic formingprocesses to a forged product in a manner that will be described later,as noted above.

The connecting shaft portion 33 as shown in FIGS. 3 and 4 has anattachment portion 33 a receiving a dust cover (not shown), and a malethread portion 33 b for connection to an associated link such as thelinks 17, 18, 19 and 21 (FIG. 1). The reference numeral 33 c denotes aflange serving as a partition between the attachment portion 33 a andthe male thread portion 33 b. A reference numeral 33 d denotes an Allenwrench receiving hole formed in the axial center of the shaft end. Acircular flat surface 32 e is provided on the smooth ball portion 32, onthe opposite side of the connecting shaft portion 33 for improvingefficiency of plastic forming and a forming dent 32 f for positioningthe operation in the die remain.

FIG. 5 is a cross sectional view of a circular blank 34 of material thatwill be formed, from the forging steps shown in FIG. 7 to the finallyfinished ball joint 31 shown in cross section in FIG. 6.

Referring now to FIG. 6 in detail, the reference numeral 35 denotesgenerally a weight reduction space formed on the inside surface of theforged product 31. The weight reduction space 35 is formed as a singlespace by interconnecting a spherical space 35 a centered onapproximately the same center as that of the external surface so as tohave approximately constant wall thickness with an elongated cylindricalspace 35 b formed coaxially with the connecting shaft portion 33.Incidentally, an annular excess material rib portion 31 b present insidethe spherical space 35 a occurs in the manufacturing process as will bedescribed later in detail.

As described above, the weight is reduced from the ball joint member 16in the region between the smooth ball portion 32 and the connectingshaft portion 33 approximately along the external surface shape to formthe space 35. As a result, excess weight is reduced to a practicalminimum. According to this example, a conventional product withoutweight reduction weighing 65 grams is lightened to 45. In addition, asthe weight reduction is made without causing recesses on the outersurface, the same external shape as that of the conventional productresults so the function and action the conventional product provides arenot impaired.

The actual forming process (forging) will now be described in detail byprimary reference to the several views of FIG. 7, that also shows theforging tools employed in each step at the lower portion of this figureand the blank formed by these tools at the upper portions of the figure.The steps are numbered in sequence, but it should be noted that thoseskilled in the art may employ different steps and/or sequences withoutdeparting from the invention.

The forging machine mainly uses in the first steps so-called two-piecesplit dies disposed to be movable in a generally axial direction towardand away from each other on both sides of the pellet-shaped forgingblank 34. The final two steps employ a three-piece split die. Thetwo-piece split die, as is well-known, has die surfaces carved inopposing faces of the split die pieces that move to and away from eachother relative to the longitudinal axis of the blank 34. The three-piecesplit die has a third die interposed between the two split die pieces.In this example, the third die of the three-piece split die is made upof several die pieces that may be separated in radial directions.

Referring now in detail to the steps shown in FIG. 7, a forging blank 34is formed in the first step shown in FIG. 7(1) by a pair of dies, apressing die 41 and a receiving die 42, movable to and away from eachother, into a first partially processed piece 43 of a roughly bulletshape as a whole with its one end having a convex portion 43 a of asemispherical outer shape. The other end is formed with a shallowcircular recess portion 43 b. This initial shaping is done to smoothenmaterial flow within the dies 41 and 42 to reduce stresses andfacilitate the forming in the next step.

In the following second step, the partially processed work 43 is workedby a forming die 44 and a receiving die 45. The partially formed piece43 is inverted as shown in FIG. 7(2) and is supported in the receivingdie 45 that has a semispherical inside bottom. Then, the recess 46 b andsurrounding wall 46 a of the work piece is extended by pressing by thepunch-shaped pushing die 44. This produces a second partially processedwork 46 of an elongated cylindrical container-like shape having acylindrical wall portion 46 a around an axial hole 46 b with its upperend open and an approximately semispherical bottom portion 46 ccontinuous with the cylindrical wall portion 46 a. As a practicalmatter, this step of forming the container-like member is not greatlydifferent from that in conventional forming method.

The third step, shown in FIG. 7(3) constitutes one of the features ofthe invention. As shown in this figure, a pressing die 47 and receivingdie 48 are employed. The bottom portion 46 c of the second partiallyprocessed work 46 is supported in the receiving die 48 having a diesurface of semispherical shape slightly greater in diameter than thebottom portion 46 c. The punch-shaped pressing die 47 is slightlygreater in diameter than the axial hole 46 b and is pressed to draw theinside round surface of the cylindrical wall portion 46 a to form acylindrical wall portion 49 a of a further reduced wall thickness, whileincreasing the inside diameter 49 b.

In the process of the pressing die 47 being pressed into the previouslyformed work piece 46, it is pressed hard against the die surface of thereceiving die 48, the bottom portion 49 b bulges outward. At the sametime, part of the material of the cylindrical wall portion 46 a flowsinto the bulged portion and expands into the die 48, so that anapproximately spherical bottom portion 49 b is formed.

Also in the process of the pressing by the pressing die 47, excessmaterial is forced out the inside surface of the cylindrical wallportion 46 a with the fore-end face of the drawing die 47 is left behindwhen the pressing die 47 is retracted to form the above-mentionedannular excess material portion 49 c rising inward from the vicinity ofthe bottom portion 44 b. In this way, the third step half-processed work49 is formed with the approximately spherical bottom portion 49 bcontinuous to one end of the thin cylindrical wall portion 49 a.

Next, in the fourth step shown in FIG. 7(4), the partially processedwork piece 49 resulting from the third step is processed with areceiving die 51 having a semispherical receiving surface, as will bedescribed in more detail shortly, and with a pressing die 52 movingtoward and away from the receiving die 51.

The die surface of the pressing die 52, as shown in the lower half ofthe drawing, has three step portions 52 a, 52 b, 52 c of increasinginside diameters, and a ceiling portion 52 d. The ceiling portion 52 dcarries an axially extending projecting member 52 e formed with a roundor hexagonal rod shape, which is decided, as will be described later.

The semispherical receiving surface, previously mentioned, of the bottomcentral portion of the receiving die 51 includes a generally flatportion 51 a of a small diameter with a small semispherical projection51 b rising in the center of the flat portion 51 a. Further, a spaceremains between the inside surface of the die and the surface of thehalf-processed work and to receive the material escaping during thetight-closed forging step. This material receiving area is indicated bythe reference numeral 51 c.

Thus, as the pressing die 52 moves toward the receiving die 51, theouter surface of a thin cylindrical wall portion 49 a is drawn upwardlyto form a portion of a further smaller diameter 54. At the same time,the upper end portion of the cylindrical wall portion 31 is depressed bythe semispherical ceiling portion 52 d of the pressing die 52, and flowsalong the wall surface while curving radially inward. Thus the wallthickness increases greatly while the outside diameter shrinks. Part ofthe material flowing at this time goes under the projecting member 52 eand its fore-end portions meet together around the center of the shaftto almost close the opening. Thus a preliminary hole 54 a for latermachining of the engagement hole 19 d is formed.

Further, the pressing force applied with the pressing die 52 during thedrawing step forms a step portion 54 b between the thin cylindrical wallportion 49 a and the shaft-shaped small diameter portion 54. Part of thesmall diameter portion 49 a located below the step portion 54 b ispushed out to the bottom portion 49 b expanded in the previous step, sothat its outside round portion expands further to form an enlargedbottom portion 53 b.

At this time, a small projection 51 b provided on a flat bottom 51 a ofthe receiving die 51 pierces into and axially supports the fourth stephalf-processed work 53. These produce at the base of the lower portion adent 53 c remaining in the center of a flat surface 53 d after theforming step. Further, the reference numeral 51 c denotes a spaceremaining between the inside surface of the die and the surface of thehalf-processed work for receiving the material escaping duringtight-closed forging step.

In this way, on condition that the semispherical die surface of thereceiving die 51 is made with some margin in diameter relative to theplanned size of the bottom portion 37, the fourth half-processed work 53having a further expanded spherical portion 53 a is formed simply byusing dies that restrict the outer shape while vertically compressingthe third step half-processed work 49 supported at the upper and loweraxial portions.

Next, in the fifth step shown in FIG. 7(5), the fourth half-processedwork 53 obtained in the previous step is further compressed in the axialdirection so that axial length is shortened while the outside diameterof the spherical portion 53 a expands further to approximate the shapeof the final forged product 31.

Here are used, like the dies used in the fourth step [FIG. 7 (4)], areceiving die 61 having a semispherical bottom portion for supportingthe spherical portion 53 a of the fourth half-processed work 53 and apressing die 62 for correcting the shape of the upper portion.

The pressing die 62, like the pressing die 52, is provided with stepportions 62 a, 62 b, 62 c, and a rod-like projection 63 for forming theengagement hole 19 d. The receiving die 61 is provided with a smalldiameter flat surface portion 61 a and a semispherical small projection61 b on the bottom portion of the die surface.

Therefore, as the receiving die 61 and the pressing die 62 approach eachother, the rod-like projection 63 engages with the preliminary hole 54 aof the fourth half-processed work 53 to form the new fifth processedpart 55, and the semispherical small projection 61 b engages with theforming dent 51 b and they are supported respectively.

The die surfaces formed on the inside surface of the pressing die 62 andthe projection 63 are configured to form the final shape of the end 33 band the tool receiving hole 33 d. Thus when the pressing step of FIG.7(5) is completed the upper portion of the spherical portion 55 a, partof the material around the rod-like projection 63 and the step portion55 b is depressed hard and the material around the tool receiving hole33 d is finished into required shape. At the same time, some of the thincylindrical wall portion 55 c is forced into the upper part of thespherical portion 55 a.

At this time, the underside part thicker than the excess material part55 c formed inside the spherical portion 53 a expands in diameter andworks to pull in the thin cylindrical wall portion 55 a that comesflowing to the excess material part 55 c. In this way, the fifthhalf-processed work 55 having the spherical portion 53 a of a furtherincreased diameter is obtained.

FIG. 7(6) shows the final, sixth step. This step employs two dies eachof which is split along the axial direction (a receiving die 71, and apressing die 72). Interposed between these two dies (71 and 72) is athird, a split die 73 interposed between the two. The split die 73 ismade up of three pieces split in the circumferential direction andmovable in radial directions relative to the axis of the work piece 55to form the finally shaped piece 33. The reference numeral 74 identifiesa rod like projection similar to the rod-like projection 63 used in theprevious step. This projection 74 is secured to the pressing die 72.

Initially, the forming dent 51 b of the fifth half-processed work piece55 is engaged with the small projection 71 b of the receiving die 71.Then the dies 71, 72, and 73 are advanced relative to each other.

This includes engaging the small diameter portion 54 of the workpiece 55with the step portion of the pressing die 72. Then the pressing die 72is advanced toward the die 73 while tightening the squeezing die 73 in aradial direction relative to the small diameter portion 54. Thusmaterial flows from the cylindrical wall portion 49 a and small diameterportion 54 into a recess 73 a provided in the squeezing die 73. As thematerial fills the recess 73 a, the material projects to form theannular flange 33 c, so that the forged product 32 is finished. Thethreaded portion 33 b is then machined in a suitable manner.

It should be readily apparent from the foregoing description that thedescribed methodology and apparatus provides a strong low cost balljoint element. However those skilled in the art will readily understandthat the metholodgy and apparatus employed therefore may be subject tovarious changes and modifications without departing from the spirit andscope of the invention, as defined by the appended claims.

1. A method of forming a ball member for a ball and joint pivotal connection being formed from a single piece comprised of a ball portion adapted to be pivotally connected within a socket formed by one of the elements to be connected and a shank portion adapted to be fixedly secured in a complimentary opening of the other element to be pivotally connected, comprising the steps of forging a solid cylindrical piece of metal into the integral ball and shank portions with complimentary closed ball shaped and cylindrical shaped cavities by forging steps.
 2. The method as set forth in claim 1, wherein the forging steps comprise an initial step of forging a cylindrical cavity opening through one end of the cylindrical piece of metal and subsequently closing its open end through another forging step.
 3. The method as set forth in claim 1, wherein the forging steps include steps of forming the ball portion on successive forging steps where the external diameter is progressively increased.
 4. The method as set forth in claim 1, wherein the forging steps include steps of progressively decreasing the diameter of an end of the cylindrical portion.
 5. The method as set forth in claim 4, wherein the forging steps comprise an initial step of forging a cylindrical cavity opening through one end of the cylindrical piece of metal and subsequently closing its open end through another forging step.
 6. The method as set forth in claim 5, wherein the forging steps include steps of forming the ball portion on successive forging steps where the external diameter is progressively increased
 7. The method as set forth in claim 6, wherein the forging steps progressively increase the diameter of the cavity in the ball portion.
 8. The method as set forth in claim 7, wherein the forging steps further form a cylindrical enlargement between the ends of the cylindrical portion.
 9. The method as set forth in claim 1, wherein the forging steps include steps of forming a cavity within the solid cylindrical piece of metal, forming an inner closed end of the cavity having an inner surface defining a hemispherical shape, and forming a cylindrical portion of the cavity extending from the closed end to an open end of the piece of metal, distal from the inner closed end.
 10. The method as set forth in claim 9 additionally comprising a step of drawing metal forming an inner surface of the cylindrical portion, toward the inner closed end.
 11. The method as set forth in claim 10, wherein the step of step of drawing metal additionally comprises drawing the metal inwardly at an upper end of the closed end to thereby transform the hemispherical shape of the closed end to enclose a partial spherical cavity that is more than a hemisphere but less than an entire sphere.
 12. The method as set forth in claim 11 additionally comprising pressing the single piece until the shape of the inner surface of the closed end is transformed into an approximately spherical shape.
 13. A method of forming a ball member for a ball and joint pivotal connection being formed from a single piece comprised of a ball portion adapted to be pivotally connected within a socket formed by one of the elements to be connected and a shank portion adapted to be fixedly secured in a complimentary opening of the other element to be pivotally connected, the method comprising the steps of: forging a cylindrical recess in a single piece of metal such that the cylindrical recess includes an open end at a first end of the single piece of metal and a closed end of the single piece of metal; forging an inner surface of the closed end to have a hemispherical shape having a terminal end and an open end connecting to the cylindrical recess; drawing metal from an inner surface of the cylindrical recess into an inwardly protruding portion at the open end of the hemispherical shape; closing the open end of the cylindrical recess by forging.
 14. The method as set forth in claim 13 additionally comprising further forging the single piece of metal until the inner closed end has an approximately spherical inner surface.
 15. The method as set forth in claim 13 additionally comprising forming the outer surface of the ball portion on successive forging steps where the external diameter is progressively increased.
 16. The method as set forth in claim 13 additionally comprising the steps of progressively decreasing an outer diameter of the portion of the single piece of metal including the cylindrical recess.
 17. The method as set forth in claim 13 additionally comprising the steps of progressively increasing an outer diameter of the portion of the single piece of metal including the closed end.
 18. The method as set forth in claim 17, wherein the steps of progressively increasing the outer diameter comprises forming the outer surface of the closed end into a ball shape.
 19. The method as set forth in claim 7, wherein the forging steps further form a cylindrical enlargement between the ends of the cylindrical portion. 